Two Chalcone Synthase Isozymes Participate Redundantly in UV-Induced Sakuranetin Synthesis in Rice

• Main Authors: Hye Lin Park, Youngchul Yoo, Seong Hee Bhoo, Tae-Hoon Lee, Sang-Won Lee, Man-Ho Cho
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: International Journal of Molecular Sciences
• Subjects: chalcone synthase; sakuranetin; rice; sakuranetin biosynthesis; phytoalexin; UV
• Online Access: https://www.mdpi.com/1422-0067/21/11/3777
• ISSN: 1661-6596; 1422-0067

<b>: </b>Chalcone synthase (CHS) is a key enzyme in the flavonoid pathway, participating in the production of phenolic phytoalexins. The rice genome contains 31 <i>CHS</i> family genes (<i>OsCHS</i>s). The molecular characterization of <i>OsCHS</i>s suggests that <i>OsCHS8</i> and <i>OsCHS24</i> belong in the bona fide CHSs, while the other members are categorized in the non-CHS group of type III polyketide synthases (PKSs). Biochemical analyses of recombinant OsCHSs also showed that OsCHS24 and OsCHS8 catalyze the formation of naringenin chalcone from <i>p</i>-coumaroyl-CoA and malonyl-CoA, while the other OsCHSs had no detectable CHS activity. OsCHS24 is kinetically more efficient than OsCHS8. Of the <i>OsCHS</i>s, <i>OsCHS24</i> also showed the highest expression levels in different tissues and developmental stages, suggesting that it is the major CHS isoform in rice. In <i>oschs24</i> mutant leaves, sakuranetin content decreased to 64.6% and 80.2% of those in wild-type leaves at 2 and 4 days after UV irradiation, respectively, even though <i>OsCHS24 </i>expression was mostly suppressed. Instead, the <i>OsCHS8</i> expression was markedly increased in the <i>oschs24</i> mutant under UV stress conditions compared to that in the wild-type, which likely supports the UV-induced production of sakuranetin in <i>oschs24</i>. These results suggest that OsCHS24 acts as the main CHS isozyme and OsCHS8 redundantly contributes to the UV-induced production of sakuranetin in rice leaves.